Sealed Rare Earth Magnet and Method for Manufacturing the Same

ABSTRACT

It is an object of the present invention to provide a rare earth magnet that will not decompose due to hydrogen embrittlement when used in a hydrogen gas atmosphere, and furthermore, does not pose the risk of contaminating a reaction bath with the surface treated film of the magnet. The present invention provides a sealed rare earth magnet comprising: a rare earth magnet; and a case of aluminum or aluminum alloy, wherein the case covers entirety of the rare earth magnet and is sealed by HIP; and the methods for manufacturing the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/063,008, filed Feb. 22, 2005, incorporated herein by reference in itsentirety, and claims the benefit of its earlier filing date under 35U.S.C. 119(e).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to sealed rare earth magnets and methodsfor manufacturing the same, and more specifically relates to sealed rareearth magnets used in motors or semiconductor manufacturing devices, andmethods for manufacturing the same.

2. Description of Related Art

Rare earth magnets have utilized in various fields such as motors andsemiconductor manufacturing devices. For example, when rare earthmagnets are utilized in motors for fuel cell vehicles, there is a riskthat the rare earth magnets will be exposed to a hydrogen gasatmosphere. In addition, etchers and the like in semiconductormanufacturing devices sometimes utilize hydrogen gas as the reactinggas. In such a case, there is a possibility that when rare earth magnetsare used in semiconductor manufacturing devices, there is a risk thatthey will be similarly exposed to the hydrogen gas atmosphere. Rareearth magnets suffer from hydrogen embrittlement. Therefore, even ifvarious anti-oxidation surface treatment methods such as nickel plating,copper plating, aluminum ion plating and resin coating are utilized onthe magnet surface, when in a hydrogen atmosphere, there is the problemof the risk that the magnet will be destroyed due to hydrogenembrittlement. As a rare earth magnet in which countermeasures are takenagainst hydrogen embrittlement, Japanese Patent Application UnexaminedPublication No. H11-087119/1999 A, which is herein incorporated byreference, discloses a rare earth magnet that has a hydrogen storagealloy, which shows a plateau pressure of 0.001 to 0.1 MPa at atemperature of 400 K and above, as a surface treatment film, wherein therare earth magnet is preferably Nd₂Fe₁₄B₁, and wherein the surfacetreatment film is preferably made by providing a Pd plating on thesurface of the Nd₂Fe₁₄B₁.

SUMMARY OF THE INVENTION

It was found that a permanent magnet provided with the above-notedsurface treatment shows no abnormalities in 100 ppm hydrogen gas.However, in a hydrogen gas atmosphere at a higher pressure, there is theproblem that the magnet material was reduced to a particulate state byhydrogen embrittlement. Furthermore, in cases in which the permanentmagnet is utilized in semiconductor manufacturing devices, when thesurface treated film is nickel or copper, there is the problem of therisk of contaminating the reaction bath.

Thus, it is an object of the present invention to provide a rare earthmagnet that will not decompose due to hydrogen embrittlement when usedin a hydrogen gas atmosphere, and furthermore, does not pose the risk ofcontaminating a reaction bath with the surface treated film of themagnet.

In one aspect of the present invention, there is provided a sealed rareearth magnet comprising: a rare earth magnet; and a case of aluminum oraluminum alloy, wherein the case covers entirety of the rare earthmagnet and is sealed by HIP.

In another aspect of the present invention, there is provided a sealedrare earth magnet comprising: a rare earth magnet; and a case ofaluminum or aluminum alloy, wherein the case covers entirety of the rareearth magnet and has substantially no pinholes.

In another aspect of the present invention, there is provided a methodfor manufacturing a sealed rare earth magnet, the method comprising thesteps of: covering a rare earth magnet or a rare earth magnet materialwith a case of aluminum or aluminum alloy; and sealing the case by HIP.

As will be described in detail below, with the present invention, bycovering a rare earth magnet with an aluminum case and sealing thepermanent magnet by HIP processing, it is possible to increase thehydrogen gas resistivity of rare earth magnets within a hydrogen gasatmosphere. Thus, it is possible to widen the range of environments inwhich the rare earth magnet can be used. Furthermore, even if the rareearth magnet is used in semiconductor manufacturing devices, the surfacetreatment of the rare earth magnet prevents contamination of thereaction bath.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the step of covering the rare earth magnetwith an aluminum case in the method for manufacturing the sealed rareearth magnet according to one embodiment of the present invention.

FIG. 2 schematically shows horizontal (A) and vertical (B)cross-sectional views of the step of sealing the aluminum case by HIPprocessing, in the method for manufacturing the sealed rare earth magnetaccording to one embodiment of the present invention.

FIG. 3 schematically shows a frontal view of the sealed rare earthmagnet according to one embodiment of the present invention.

FIG. 4 schematically shows a rotor of a four pole IPM motor, wherein thesealed magnet according to the present invention is utilized.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention are described below with referenceto the attached drawings. The embodiments described below do not limitthe present invention.

As described above, the present invention provides a sealed rare earthmagnet comprising a rare earth magnet; and a case of aluminum oraluminum alloy (also referred to below simply as an “aluminum case”),wherein the case covers entirety of the rare earth magnet and is sealedby HIP processing.

Examples of rare earth magnets that may be utilized in the presentinvention comprise R—Co-based rare earth magnets and R—Fe—B-based rareearth magnets. Here, R represents a rare earth metal, and morespecifically comprises the 15 elements having an atomic number fromnumber 57 to number 71 (the lanthanides: lanthanum (La), cerium (Ce),praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu),gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu)), and number 21scandium (Sc) and number 29 yttrium (Y). It is particularly preferablethat one or more selected from the group consisting of Y, La, Ce, Pr,Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu is used as R.

Here, “R—Co-based rare earth magnets” refer to a material of acomposition that contains one or more rare earth elements R and Co,which comprises a composition in which one part of the Co is substitutedwith Fe. More specifically, R—Co-based rare earth magnets compriseRCo₅-based and R₂Co₁₇-based ones and the like. However, most of theR—Co-based rare earth magnets in actual use are R₂Co₁₇-based ones.R₂Co₁₇-based rare earth magnets usually, but not exclusively, comprise20 to 30% R, 5 to 30% Fe, 3 to 10% Cu and 1 to 5% Zr, with the remainingportion Co based on weight percent. Not exclusively, the R₂Co₁₇-basedrare earth magnet may be manufactured as follows. First, the rawmaterial metal is weighed, melted, and cast, and obtained alloy isfinely crushed to an average particle diameter of 1 to 20 μm to obtainR₂Co₁₇-based rare earth permanent magnet powder. The R₂Co₁₇-based rareearth permanent magnet powder is molded within a magnetic field,subsequently sintered at 1100 to 1250° C. for 0.5 to 5 hours, thensubjected to solution heat treatment for 0.5 to 5 hours at a temperatureless than the sintering temperature by 0 to 50° C., and finallysubjected to aging treatment. Aging treatment is usually performed inthe first step by maintaining the magnet at 700 to 950° C. for aspecified time period, followed by continuously cooling or step-wiseaging treatment. The RCO₅-based magnets usually comprise 30 to 40 wt % Ras the principal components with the remaining portion Co based onweight percent.

Furthermore, R—Fe—B-based rare earth magnets have a compositioncontaining one or more rare earth elements R; iron, or iron and Co;boron; and optional additives. R—Fe—B-based rare earth magnets areusually, but not exclusively, comprise 5 to 40% R, 50 to 90% Fe and 0.2to 8% B based on weight percent. In order to improve the magneticproperties, additive elements such as C, Al, Si, Ti, V, Cr, Mn, Co, Ni,Cu, Zn, Ga, Zr, Nb, Mo, Ag, Sn, Hf, Ta and W are often added toR—Fe—B-based rare earth magnets. It is usual that the amount of theseadditives is 30 wt % or less in the case of Co, and 8 wt % or less inthe case of other elements. The addition of more additives than this mayrun the risk of conversely degrading the magnetic properties. Notexclusively, R—Fe—B based rare earth magnets may be manufactured asfollows. First, the raw material metal is weighed, melted, cast, andobtained alloy is finely crushed to an average particle diameter of 1 to20 μm to obtain R—Fe—B-based rare earth permanent magnet powder. TheR—Fe—B-based rare earth permanent magnet powder is molded within amagnetic field, subsequently sintered at 1100 to 1200° C. for 0.5 to 5hours, followed by aging treatment at 400 to 1000° C. to obtain theR—Fe—B-based rare earth magnet.

Furthermore, usually, in case of R—Co-based rare earth magnets, magnetshaving an energy product of 18 to 34 MGOe, and in case of R—Fe—B-basedrare earth magnets, magnets having an energy product of 26 to 52 MGOeare used most effectively. The shape of the rare earth magnet is notlimited, and, any desired shape can be used, such as cubic, rectangular,columnar, cylindrical and fan-shaped magnets.

The sealed rare earth magnet according to the present invention alsocomprises a case of aluminum or aluminum alloy wherein the case coversentirety of the rare earth magnet and is sealed by HIP processing. Forthe case for covering the magnet, pure aluminum or aluminum alloy isused. This is because even if the magnet is utilized in semiconductormanufacturing devices or the like, there is no risk of contaminating thereaction bath of the semiconductor manufacturing device. In other words,this is because the reaction bath of semiconductor manufacturing devicesis usually made of aluminum and therefore even if the magnet accordingto the present invention is contained internally for providing magneticfields used in the reaction processes and the like, there is nocontamination of the reaction bath. In addition, as described in detailbelow, by using an aluminum case, it is possible to carry out HIPprocessing at a temperature of about 500° C., and thus it is possible toseal the magnet without affecting the magnetic characteristics of themagnet. Suitable aluminum alloys for the present invention compriseAl—Cu, Al—Mn, Al—Si, Al—Mg, Al—Mg—Si and Al—Zn-based aluminum alloys.Especially, alloys that are easily joined by HIP processing comprisepure aluminum and Al—Mn and Al—Mg—Si-based alloys. More specifically,they comprise materials with the JIS (Japanese Industrial Standards)material numbers A1100, A3003 and A6061.

The shape of the case is not limited, and preferably selected fromshapes such as rectangular, cubic, columnar, and cylindrical shapes,depending on the shape of the magnet. It should be noted that cases inwhich a magnet is covered may comprise a case portion and a lid portion.Furthermore, it is preferable that the shape inside the case is matchedto the shape of the magnet. The thickness of the aluminum is notlimited, however the greater the thickness, the more able it is toprevent penetration of hydrogen. More specifically, not exclusively, itis preferable that the thickness of the aluminum is 0.5 to 10 mm.

As noted above, the sealed rare earth magnet according to the presentinvention can be manufactured by the steps of covering a rare earthmagnet or a rare earth magnet material with a case of aluminum oraluminum alloy; and sealing the case by HIP processing. FIG. 1schematically shows the step of covering the rare earth magnet with analuminum case in the method for manufacturing the sealed rare earthmagnet according to one embodiment of the present invention. Morespecifically, by processing the aluminum material, it is possible tofabricate a case portion and a lid portion in which the magnet isinserted. Subsequently, as shown in FIG. 1, by inserting a rare earthmagnet 2 into an aluminum case portion 4 and shutting the open portionof the case portion with a lid portion 5, the rare earth magnet can becovered by the aluminum case. It should be noted that, as is describedbelow, the rare earth magnet can be magnetized before or after the stepof covering with the aluminum case. In the latter case, it is possibleto cover the rare earth magnet material with the aluminum case. In asimilar manner, the rare earth magnet can be magnetized before or afterthe step of sealing with HIP processing.

In particular it is an object of the present invention to obtain amagnet in which hydrogen embrittlement does not occur, and furthermore,rare earth permanent magnets are particularly susceptible to degradationby oxidation. Therefore, when the magnet is inserted into the case, itis preferable that the concentration of oxygen in the magnet is 100 to10,000 ppm and is more preferably 500 to 6,000 ppm. In a similar manner,when the magnet is inserted into the case, it is preferable that theconcentration of hydrogen in the magnet is 50 ppm or less, and is morepreferably 10 ppm or less.

Moreover, the sealed rare earth magnet according to the presentinvention is sealed by HIP processing. HIP processing is also known ashot isostatic pressing or hot isotropic pressing, and is a technology inwhich an object to be processed is pressured by applying a highisotropic pressure at high temperature via a pressure medium such as agas. FIG. 2 schematically shows horizontal (A) and vertical (B)cross-sectional views of the step of sealing the aluminum case by HIPprocessing, in the method for manufacturing the sealed rare earth magnetaccording to one embodiment of the present invention. As shown in FIG.2, for example, when the aluminum case comprises the case portion 4 andthe lid portion 5 as described above, by HIP processing these parts itis possible to join the case portion in which the magnet 2 is insertedand the lid portion.

It is preferable that HIP processing is performed under the followingconditions. That is to say, it is preferable that the processingtemperature is 0.6 or more times the melting point of aluminum or thealuminum alloy (approximately 660° C.), (for example, if the meltingpoint is 600° C., the processing temperature is 396° C. or greater) andless than or equal to the melting point, and more specifically, ispreferably 500 to 600° C. Furthermore, for the processing time, thelonger the time, the further the joining becomes. More specifically, itis preferable that the processing time is 1 to 3 hours. Furthermore, itis preferable that the processing pressure is 1,000 to 2,000 kg/cm².Furthermore, it is preferable that the pressure medium for applyingisotropic pressure to the object to be processed is a gas such as argon(Ar). This is because under these conditions the magneticcharacteristics of the magnetic material are less liable to change.

According to the present invention, by sealing by HIP processing, it ispossible to completely seal a separated aluminum case and to preventpenetration of hydrogen without change in the magnetic properties of themagnet material. Specifically, with the present invention, because thepermanent magnet is completely sealed by aluminum, there is no contactbetween the magnet and hydrogen gas. On the other hand, since processessuch as CIP (Cold Isostatic Pressing) do not ensure good contact of theseparated aluminum case, they cannot prevent the penetration of hydrogengas.

Furthermore, HIP processing is preferable because pinholes can beprevented. Welding is an example of a method for sealing the case.However, welding is not preferable, since it cannot prevent pinholes,and hydrogen may penetrate through the pinholes. On the other hand,since HIP processing has the effect of pressing out and removing airholes within the material, pinholes are not substantially present in thecase of the present invention. It should be noted that the presence orabsence of pinholes can be confirmed as follows. That is to say, theycan be measured by visual inspection, or by devices such as detectiondevices that use CCD image analysis or detection devices that use lowfrequency pulses.

Moreover, as an example of a method for sealing the case, there is amethod which uses seal material such as O-rings. However when sealmaterials are used, there is the problem that the case increases in sizeby the size of the seal portion.

Moreover, with the present invention, after HIP processing, it ispossible to machine the case and its surroundings where necessary. FIG.3 schematically shows a frontal view of the sealed rare earth magnetaccording to one embodiment of the present invention. A sealed magnet 1shown in FIG. 3 is an example in which tap holes 6 have been opened bymachining in an aluminum case 3 covering the magnet 2. Since the rareearth magnet is a sintered body, and thus has mechanically fragilecharacteristics, the magnet can not be tapped. However, with the sealedmagnet according to the present invention, since the rare earth magnetis covered by the aluminum case, tap holes can be provided in thealuminum case, and thus it is possible to mechanically fix the rareearth magnet to a device.

Furthermore, with the present invention, after HIP processing, it isalso possible to perform alumite treatment or the like. By alumitetreatment, it is possible to improve properties such as the corrosionresistance, hardness, abrasion resistance and heat resistance of thesealed rare earth magnet. The conditions for alumite treatment can bearranged by one skilled in the art as appropriate in accordance with theobject as exemplified as follows. That is to say it may be processed bydegreasing, rinsing, etching, rinsing, neutralizing, electrolyzing(alumite treatment), rinsing, colouring, rinsing, sealing, hot waterrinsing and drying.

Thus, the sealed magnet according to the present invention can preventhydrogen embrittlement, and can be effectively used in a wide range offields such as magnetic circuits, motors and semiconductor manufacturingdevices. Below, the sealed magnet according to the present inventionutilized in a rotor of a four pole IPM (interior permanent magnet) motoris illustrated. FIG. 4 schematically shows a rotor of a four pole IPMmotor, wherein the sealed magnet according to the present invention isutilized. Not exclusively, it is possible to provide a rotor 10 of themotor by providing rectangular holes in a rotor yoke 11 and insertingmagnetized magnets into these holes, as illustrated in FIG. 4. Morespecifically, not exclusively, the ring-shaped rotor yoke 11 has aplurality of openings for inserting the sealed magnet 1 according to thepresent invention. The openings are disposed concentrically with therotor yoke in regular intervals. The sealed magnets according to thepresent invention comprising the rare earth magnets 2 sealed in thealuminum cases 3 are inserted in the openings. Here, the magnetizationdirection of the each magnet is the radial direction, and is opposite ofadjacent magnets. In FIG. 4, the magnetization direction of the magnetsis indicated by arrows. Furthermore, the magnetization of the magnetsmay be carried out after the step of sealing by HIP processing andbefore assembling the rotor, or after assembling the rotor. That is tosay, magnetized sealed magnets may be inserted in the rotor yoke, or ifa dedicated magnetization jig is prepared, magnetization may beperformed after inserting the magnets into the rotor yoke.

EXAMPLES

Working examples of the present invention are described below withreference to the attached drawings. The examples described below do notlimit the present invention.

As the present working example, sealed magnets were manufactured asgiven below. That is to say, as schematically shown in FIG. 2, analuminum case comprising a case portion and a lid portion was used. Forthe aluminum case, a material of aluminum alloy A6061 was used. For therare earth magnets, a Sm₂Co₁₇ magnet was used as the R₂Co₁₇-basedmagnet, and an Nd₂—Fe₁₄—B magnet was used as the R—Fe—B-based magnet.For HIP processing, Ar gas was used as the pressure medium andprocessing was performed for 1 hour at a pressure of 1000 kg/cm² and atemperature of 500° C. 500° C. is the lower limit of the heat treatmenttemperature of the magnet, namely, it corresponds to the heat treatmenttemperature for generating the magnetic properties of the ND₂-Fe₁₄—Bmagnet, but since the processing time was about one hour, there were nochanges in the magnetic properties. Below, the working example in whichthe Sm₂Co₁₇ magnet was used is taken as working example 1, and theworking example in which the Nd₂—Fe₁₄—B magnet was used is taken asworking example 2.

For comparison, Sm₂Co₁₇ magnets, wherein the magnet has had no surfacetreatment (comparative example 1), wherein the magnet is nickel platedwith a film thickness of 20 μm (comparative example 2), and wherein themagnet is copper plated with a film thickness of 20 μm (comparativeexample 3) were used. In a similar manner, for comparison, Nd₂—Fe₁₄—Bmagnets, wherein the magnet has had no surface treatment (comparativeexample 4), wherein the magnet is nickel plated with a film thickness of20 μm (comparative example 5), and wherein the magnet is copper platedwith a film thickness of 20 μm (comparative example 6) were used.

For the hydrogen gas test, the sealed magnets according to the workingexamples, and the magnets according to the comparative examples wereexposed at a pressure of 3 MPa for one day, or at a higher pressure of15 MPa for one day or for seven days, subsequently observing the stateof the magnets. The test temperature was 25° C., and the results areshown in Table 1.

TABLE 1 Hydrogen gas test Working example/ 3 MPa 15 MPa 15 Mpa MagnetComparative example 1 day 1 day 7 days Sm₂Co₁₇ Comparative NAD destroyeddestroyed magnet example 1 Comparative NAD destroyed destroyed example 2Comparative NAD NAD destroyed example 3 Working example 1 NAD NAD NADNd—Fe—B Comparative destroyed destroyed destroyed magnet example 4Comparative NAD destroyed destroyed example 5 Comparative NAD NADdestroyed example 6 Working example 2 NAD NAD NAD NAD: nothing abnormaldetected

As shown in Table 1, no abnormalities were observed in the sealed magnetaccording to the present invention, even after experiencing the severeconditions of 15 MPa for seven days. On the other hand, in the case ofthe Nd magnet on whose magnet surface no treatment was performed, themagnet was destroyed after just one day at 3 MPa (comparative example4). In the case of the Sm magnet, hydrogen embrittlement was less thanthe Nd magnet, but it was destroyed at 15 MPa (comparative example 1).Hydrogen embrittlement is prevented by nickel plating and copperplating, but those magnets were destroyed when the treated time wasincreased (comparative example 2, 3, 5 and 6). It seems that hydrogenembrittlement proceeded because of pinholes in the plating film andhydrogen penetration. On the other hand, as noted above, HIP processinghas the effect of squeezing out and removing air holes within thematerial, and thus there were no pinholes in the case of the presentinvention.

As given above, with the present invention, by covering the surface of arare earth magnet with an aluminum case and sealing the permanent magnetby HIP processing, it is possible to increase the hydrogen gasresistivity of the rare earth magnet in a hydrogen gas atmosphere. Thus,it is possible to widen the range of environments in which the rareearth magnet can be used. Furthermore, in semiconductor manufacturingdevices, by treating the surface of the rare earth magnet, there is nocontamination of the reaction bath.

1. A sealed rare earth magnet comprising: a rare earth magnet; and acase of aluminum or aluminum alloy, wherein the case covers entirety ofthe rare earth magnet and is sealed by HIP.
 2. The sealed rare earthmagnet according to claim 1, wherein the magnet has a size and shapeapproximating the interior shape of the case.
 3. The sealed rare earthmagnet according to claim 1, wherein the rare earth magnet is aR—Co-based or R—Fe—B-based rare earth magnet, wherein R is a rare earthmetal.
 4. The sealed rare earth magnet according to claim 1, wherein thecase comprises a lid portion sealed to a case portion.
 5. The sealedrare earth magnet according to claim 1, wherein the case has a thicknessof 0.5 to 10 mm.
 6. The sealed rare earth magnet according to claim 4,further comprising a seal between the case and lid portion that ischaracterized by the absence of welding.
 7. The sealed rare earth magnetaccording to claim 1, wherein the rare earth magnet is a R—Co-based rareearth magnet and wherein R is selected from the group consisting oflanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), europium(Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc)and yttrium (Y).
 8. The sealed rare earth magnet according to claim 1,wherein the rare earth magnet is a R—Fe—B-based rare earth magnet inwhich R is a rare earth metal.
 9. A method for manufacturing a sealedrare earth magnet, the method comprising the steps of: covering a rareearth magnet or a rare earth magnet material with a case of aluminum oraluminum alloy; and sealing the case by HIP, wherein the magnet has asize and shape approximating the interior shape of the case.
 10. Themethod according to claim 9, wherein the case has a thickness of 0.5 to10 mm.
 11. The method according to claim 9, wherein the case comprises alid portion sealed to a case portion, and a seal between the case andlid portion that is characterized by the absence of welding.
 12. Themethod according to claim 9, The sealed rare earth magnet according toclaim 3, wherein the rare earth magnet is a R--Co-based rare earthmagnet and wherein R is selected from the group consisting of lanthanum(La), cerium (Ce), praseodymium (Pr), neodymium (Nd), europium (Eu),gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc) andyttrium (Y).
 13. The method according to claim 9, The sealed rare earthmagnet according to claim 3, wherein the rare earth magnet is aR—Fe—B-based rare earth magnet in which R is a rare earth metal.
 14. Themethod according to claim 9, The sealed rare earth magnet according toclaim 3, wherein the rare earth magnet is a R—Fe—B-based rare earthmagnet and wherein R is selected from the group consisting of lanthanum(La), cerium (Ce), praseodymium (Pr), neodymium (Nd), europium (Eu),gadolinium (Gd), terbium (Tb), samarium (Sm), dysprosium (Dy), holmium(Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium(Sc) and yttrium (Y).
 15. The method according to claim 9, The sealedrare earth magnet according to claim 3, wherein the concentration ofoxygen in the interior of the case is between 500 to 6,000 ppm.
 16. Themethod according to claim 9, wherein the concentration of hydrogen inthe interior of the case less than 50 ppm.
 17. The method according toclaim 9, wherein the concentration of hydrogen in the interior of thecase less than 10 ppm.